Silicon carbide powder for producing silicon carbide single crystal and a method for producing the same

ABSTRACT

A silicon carbide powder for the production of a silicon carbide single crystal has an average particle diameter of 100 μm or more and 700 μm or less and a specific surface area of 0.05 m 2 /g or more and 0.30 m 2 /g or less. A method for producing a silicon carbide powder for the production of the silicon carbide single crystal including sintering a silicon carbide powder having an average particle diameter of 20 μm or less under pressure of 70 MPa or less at a temperature of 1900° C. or more and 2400° C. or less and in a non-oxidizing atmosphere, thereby obtaining a sintered body having a density of 1.29 g/cm 3  or more; adjusting particle size by means of pulverization of the sintered body; and removing impurities by means of an acid treatment.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2010˜254378, filed on Nov. 15,2010 and PCT International Application PCT/JP2011/075930, filed on Nov.10, 2011, the entire contents of which are incorporated herein byreference.

FIELD

The present invention is related to a silicon carbide powder forproducing silicon carbide single crystal and a method for producing thesilicon carbide powder.

BACKGROUND

Conventionally, a sublimation recrystallization method (Modified LelyMethod) in which silicon carbide powder which is a raw material issublimed under high temperature conditions of 2000° C. or more and asingle crystal is grown on a silicon carbide seed crystal is known as amethod of producing silicon carbide powder single crystal (Yu. M Tairovand V. F. Tsvetkov, Journal of Crystal Growth vol. 52 (1981) pp.146˜150).

In addition, it is also known that many crystal defects are produced bymixing impurities within a single crystal in the case where siliconcarbide powder including a large amount of impurities is used in asublimation recrystallization method.

The Acheson process and chemical vapor deposition method are known asmethods of producing silicon carbide powder. However, there is a problemof impurities when the silicon carbide powder is obtained using theAcheson method and low productivity when the silicon carbide powder isobtained using a chemical vapor deposition method.

In addition, a method of producing silicon carbide powder for producingsilicon carbide single crystal is disclosed (patent document 1) in whicha mixed product of a liquid shaped silicon compound and an organiccompound which produces carbon by heating is heated and reacted and thecontained amount of each impurity element is 0.5 ppm or less.

In addition, silicon carbide powder for producing silicon carbide singlecrystal is required to have a relatively large average particle diameterin order to maintain a stable sublimation rate under a single crystalgrowth condition. For example, an average particle diameter of 10˜500 μmis disclosed in Japanese Laid Open Patent H9˜48605.

SUMMARY

The present invention provides a silicon carbide powder which displays ahigh and stable sublimation rate during single crystal growth by meansof a sublimation recrystallization method; and a method for producingthe silicon carbide powder.

The present invention adopts the following means in order to solve theproblems described above.

(1) A silicon carbide powder for producing a silicon carbide singlecrystal including an average particle diameter of 100 μm or more and 700μm or less and a specific surface area of 0.05 m²/g or more and 0.30m²/g or less.(2) The silicon carbide powder for producing a silicon carbide singlecrystal according to (1) wherein primary particles having an averageparticle diameter of 5 μm or more and 200 μm or less are sintered.(3) A method for producing a silicon carbide powder for the productionof the silicon carbide single crystal according to (1) further includingsintering a silicon carbide powder having an average particle diameterof 20 μm or less under pressure of 70 MPa or less at a temperature of1900° C. or more and 2400° C. or less and in a non-oxidizing atmosphere,thereby obtaining a sintered body having a density of 1.29 g/cm³ ormore; adjusting particle size by means of pulverization of the sinteredbody; and removing impurities by means of an acid treatment.(4) The method for producing a silicon carbide powder for the productionof a silicon carbide single crystal according to (1) wherein the siliconcarbide powder is obtained by heating and sintering a raw material mixedproduct at a temperature of 1800° C. or more and 2300° C. or less undera non-oxidizing atmosphere condition using 5% by mass or more and 50% bymass or less of a silicon carbide powder with average particle diameterof 20 μm or more with a silicon source and a carbon source averageparticle diameter of 20 μm or more.(5) The method for producing a silicon carbide powder for the productionof a silicon carbide single crystal according to (1) further includingproducing the silicon carbide powder by heating and sintering metalsilicon and a carbon source with an average particle diameter of 100 μmor more and 700 μm or less under a non-oxidizing atmosphere condition ata temperature of 1300° C. or more and 1400° C. or less; andpost-processing the silicon carbide powder by heating at a temperatureof 1800° C. or more and 2300° C. or less under a non-oxidizingatmosphere condition.(6) The method for producing a silicon carbide powder for the productionof a silicon carbide single crystal according to (5) wherein the carbonsource is an organic compound and the organic compound is carbonized byheating at a temperature of 500° C. or more and 1000° C. or less under anon-oxidizing atmosphere condition before producing the silicon carbidepowder heating and sintering.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the characteristics of a silicon carbide powder related toone example of the present invention;

FIG. 2 shows the characteristics of a silicon carbide powder related toone embodiment of the present invention;

FIG. 3 shows the characteristics of a silicon carbide powder related toone embodiment of the present invention; and

FIG. 4 shows the growth of a silicon carbide single crystal related toone embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

A high and stable sublimation rate is demanded as a characteristic of asilicon carbide powder for producing a silicon carbide single crystal.For the reasons described above, the silicon carbide powder of thepresent invention has an average particle diameter of 100 μm or more and700 μm or less and a specific surface area of 0.05 m²/g or more and 0.30m²/g or less. In the case where the average particle diameter is lessthan 100 μm or the specific surface area exceeds 0.30 m²/g, thesublimation rate (2000° C. or more and 2500° C. or less) when producinga silicon carbide single crystal is high during the sublimation initialstage. However, the specific surface area decreases as sintering of thesilicon carbide powder gradually progresses and the sublimation ratedrops. On the other hand, in the case where the average particlediameter exceeds 700 μm or the specific surface area is less than 0.05m²/g, the specific surface area of the silicon carbide itself decreasesand this reduces the sublimation rate which is not desirable.

In addition, the silicon carbide powder of the present invention has aparticle state in which pairs of primary particles with particlediameter of 5 μm or more and 200 μm or less are sintered. If the primaryparticle diameter of the silicon carbide powder is less than 5 μm orexceeds 200 μm, the strength of the silicon carbide powder decreases andit is not possible to maintain the particle state when handling which isnot desirable.

Furthermore, because the silicon carbide powder of the present inventionhas a contained amount of each impurity of 1 ppm or less, crystaldefects are few and it is possible to use the silicon carbide powder asa raw material of a silicon carbide single crystal with excellentconductivity control. Here, an impurity element is an element belongs togroup 1 to group 16 and in the periodic table of the 1989 IUPACInorganic Chemical Nomenclature Revised Edition and has an atomic numberof three or more except atomic numbers 6˜8 and 14. In the presentinvention, the contained amount of Li, B, Na, Mg, Al, P, K, Ca, Ti, V,Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Mo, Pd, Cd, Sb, Ba and W is measured.

A number of producing methods of the silicon carbide powder of thepresent invention are exemplified.

(Sintered Powder Crushing Method)

A producing method wherein a silicon carbide sintered body is producedby sintering the silicon carbide powder, the particle size is adjustedby crushing the obtained silicon carbide sintered body and impuritiesmixed in during the crushing process are removed using an acid treatmentcan be given as an example of a first producing method of the siliconcarbide powder of the present invention. This is described in detailbelow.

Either an α type silicon carbide or β type silicon carbide can be usedas the silicon carbide used in the sintered body creation process. Highgrade purification is easy if a high purity silicon carbide powder isused and reducing the contained amount of each impurity to a few ppm ofless is preferred. An average particle diameter of 20 μm or less ispreferred and 10 μm is desirable considering sintering performance. Whenaverage particle diameter exceeds 20 μm, the contact area betweenadjacent powder particles decreases and sintering becomes insufficient.In addition, because the surface amount of oxygen increases when theparticle diameter is small causing a decrease in sintering performance,the lower limit value of particle diameter is preferred to be 0.1 μm ormore and more preferably 0.4 μm or more.

In addition, in a conventional producing method, a metal auxiliary agentis added in the sintering of the silicon carbide with the aim ofdensification. However, in the present invention, it is preferred thatthe silicon carbide is sintered without using a metal auxiliary agentfrom the view point of reducing impurities.

The above described silicon carbide powder is filled into a metal moldand a compact body is created. The compact metal mold which is used hereis preferred to be a metal mold having a part or all of the mold beinggraphite so that the compact and the metal sections of the metal mold donot contact considering the purity of the sintered body to be obtained.The compact which is obtained is pressure sintered under a non-oxidizingatmosphere and a sintered body is created. A hot press sintering methodis available as the pressure sintering method.

In a hot press sintering method the sintering temperature is 1900° C. ormore and 2400° C. or less and more preferably 2000° C. or more and 2200°C. or less. If the sintering temperature is less than 1900° C., thedensity of the sintered body is insufficient and if the sinteringtemperature exceeds 2400° C., the silicon carbide raw material begins tosublime which is not desirable. The applied pressure is 70 MPa or less.In the case where no pressure is applied or the applied pressure is low,the density of the sintered body to be obtained is low and therefore anapplied pressure of 10 MPa or more is preferred. In addition, if theapplied pressure exceeds 70 MPa, the hot press fixtures such as a diceor punch etc can become damaged which is not desirable consideringproducing efficiency.

The heating time during the sintering process is selected from a timeperiod according to type of silicon carbide powder which is filled orthe density of the sintered body to be obtained and a maximumtemperature is preferred to be maintained in a range of 1 hour or moreand 4 hours or less.

The obtained silicon carbide sintered body is crushed using a crushersuch as a hammer mill, a bantam mill or a jaw crusher for example and asilicon carbide powder with an average particle diameter of 100 μm ormore and 700 μm or less is obtained by separation using a sieve. It ispossible to use acid cleaning such as hydrochloric acid or hydrofluoricacid or a mixed acid of hydrofluoric acid and nitric acid to remove theimpurities that are mixed in during the crushing process.

The density of the silicon carbide sintering is 1.29 g/cm³ (relativedensity 40%) or more. Here, relative density is a value calculated witha theoretical density of 3.22 g/cm³ given as 100%. If the relativedensity exceeds 40%, mechanical strength of the sintered body decreases,the occurrence of fine particles in the following crushing processincreases and productivity decreases which is not desirable. Inaddition, although it is possible to use a densified sintered body, inthe case where a porous sintered body (relative density of 40% or more)with a low density is crushed, it is possible to obtain a powder with ahigher specific surface area. From this view point, the relative densityof the sintered body of the present invention is preferred to be 60% ormore and 80% or less.

(Nucleus Addition Method)

A method of heating and sintering a source material mixed product ofsilicon carbide powder used as the silicon source and carbon source canbe given as an example of a second producing method of the siliconcarbide powder of the present invention. This is explained in detailbelow.

Metal silicon, silicon nitride, silicon oxide, liquid shaped siliconcompound (for example, tetraalkoxysilane or its polymer) and graphitepowder, carbon black, or an organic compound with remaining carbon dueto heating (for example, phenol resin or fran resin) are available asthe as the silicon and carbon sources for producing a silicon carbidepowder. Metal silicon/carbon black, silicon nitride/carbon black arepreferred as a combination of raw materials considering handling andpurity of the silicon carbide powder after heating and sintering.

In the case of using metal silicon/carbon black, silicon nitride/carbonblack, the mol ratio (C/Si ratio) of the silicon and carbon source ispreferred to be 0.8 or more and 1.5 or less and more preferably 0.9 ormore and 1.1 or less. When the C/Si ratio is less than 0.8, non-reactedSi often remains and when the C/Si ratio exceeds 1.5, non-reacted Coften remains and a removal process is required.

Silicon carbide powder used as a raw material is preferred to have anaverage particle diameter of 20 μm or more. In addition, silicon carbidepowder of a source material mixed product is preferred to be 5% by massor more and 50% by mass or less. A source material mixed product isheated and sintered under a non-oxidizing atmosphere.

The silicon carbide powder used as a raw material selectively becomesthe start point for particle formation when heated and sintered andlarge secondary particles are formed when sintering is promoted. In thecase where average particle diameter of the silicon carbide to be addedis less than 20 μm, the particle diameter of the silicon carbide powderwhich is obtained by sintering decreases which is not desirable.Although there is not upper limit to the average particle diameter ofthe silicon carbide to be added, because coarsening effects due toparticle growth and sintering are not significantly shown when theparticle diameter is too large, the average particle diameter ispreferred to be 200 μm or less.

While a silicon carbide or β silicon carbide can be used as the siliconcarbide powder used as a raw material, because β silicon carbide isproduced in the producing method of the present invention, the use of βsilicon carbide powder is preferred. Furthermore, using β siliconcarbide powder producing from the same raw material as the siliconsource and carbon source used to produce the silicon carbide powder ismore preferable.

The silicon carbide powder used as a raw material within a raw materialmixed product is preferred to be 5% by mass or more and 50% by mass orless. In the case where the silicon carbide powder is less than 5% bymass, formation and particle growth of the silicon carbide particlesoccurs anew in parts other than the silicon carbide powder, sinteringprogresses and secondary particles do not achieve a sufficient particlediameter, and when the silicon carbide powder is more than 50% by mass,the starting points of particle growth increase and particle growtheffects decrease which is not desirable.

In the present invention, a source material mixed product added withsilicon carbide powder is preferred to be heated and sintered at atemperature of 1800° C. or more and 2300° C. or less and more preferably1900° C. or more and 2100° C. or less. If the heating temperature isless than 1800° C., particle growth and sintering of particle pairs areinsufficient and when the heating temperature exceeds 2300° C.,sublimation of the silicon carbide which is produced begins which is notdesirable.

In addition, although the heating time during heating and sintering isselected from a time range so that non-reactive objects do not exist andwhere particle growth and sintering of particle pairs progresses, thetime period at a maximum temperature is preferred to be maintained in arange of 1˜10 hours.

By performing a separation process of the silicon carbide powder whichis obtained by the method described above using a sieve for example, asilicon carbide powder with an average particle diameter of 100 μm ormore and 700 μm or less is obtained. Furthermore, by repeating the abovedescribed process a further one time or more using the silicon carbidepowder which is obtained, it is possible to obtained a coarser siliconcarbide powder.

(Solid-Phase Reaction Method)

Uniformly covering an organic compound with remaining carbon whichbecomes a carbon source due to heating, on a metal silicon which is asilicon source, heating and sintering at a metal silicon melting pointtemperature (1410° C.) or less under a non-oxidizing atmosphere toobtain a silicon carbide powder and heating the obtained silicon carbidepowder at a higher temperature than that described above under anon-oxidizing atmosphere is an example of a third producing method ofthe silicon carbide powder of the present invention. This is describedin detail below.

Considering the purity of the silicon carbide powder after heating andsintering, the metal silicon used as a raw material is preferred to havea high grade purity and the contained amount of each impurity ispreferred to be reduced to a few ppm or less. In addition, consideringthe particle diameter of the silicon carbide powder which is produced asa result of heating and sintering, the particle diameter of the metalsilicon is preferred to be 100 μm or more and 700 μm or less. Inaddition, in the case of using a metal silicon having a particlediameter which exceeds 700 μm, a sintering reaction does not proceedefficiently, non-reacted metal silicon still remains and the reactionrate drops. When the particle diameter is less than 100 μm, a siliconcarbide powder with an average particle diameter of 100 μm or more and700 μm or less and a specific surface area of 0.05 m²/g or more and 0.30m²/g or less cannot be obtained which is not desirable.

While organic compounds with residual carbon due to heating areavailable to be used as the carbon source, it is also possible to useresins such as a phenol resin, fran resin, epoxy resin and xylene resinetc. While a liquid shaped material at normal temperature or a softeningor liquid shaped material due to heating such as thermoplasticity orthermal melting are mainly used, among these a resol type phenol resinis favorable considering the purpose of covering a metal silicon.

When uniformly mixing a metal silicon and carbon source, a solidmaterial formed by curing a mixed product of the metal silicon andcarbon source is preferred. For example, in the case where a liquidshaped carbon source is used, a mixed product of the metal silicon andcarbon source is cured and following this the silicon carbide issintered. Examples of the curing method are a cross linking method byheating and a curing method by a curing catalyst. In the case where thecarbon source is a phenol resin, acids such as toluenesulfonic acid,maleic acid, maleic acid anhydride and hydrochloric acid can be used asa curing catalyst.

In the producing method of the present invention, it is preferred that acarbonizing process is performed for heating a mixed product of a metalsilicon and carbon source in advance under a non-oxidizing atmosphere.When a heating carbonizing process is performed, it is possible toselect a heating temperature according to the type of organic compoundof the carbon source. However, a heating temperature of 500° C. or moreand 1000° C. or less is preferred. In addition, a heating time of 30minutes or more and 2 hours or less is preferred. If the heating time isless than 30 minutes, the carbonizing process is insufficient andimprovements in the effects of the invention are not observed if heatingis performed for over 2 hours. In addition, it is possible to usenitrogen or argon etc in the on-oxidizing atmosphere.

In the producing, method of the present invention, the mole ratio (C/Si)between silicon and carbon source of a mixed product of a metal siliconand carbon source is defined by a carbon product intermediate obtainedby carbonizing from the raw material mixed product and its value ispreferred to be 0.8 or more and 1.5 or less and more preferably 0.9 ormore and 1.1 or less. In the case where the C/Si is less than 0.8,non-reacted Si remains and the reaction rate decreases and in the casewhere the C/Si exceeds 1.5, a large amount of non-reacted C remains anda removal process becomes necessary which is not desirable.

Silicon carbide powder is produced by heating and sintering a rawmaterial mixed product obtained by a carbonizing process. In thesintering process, sintering is performed at a temperature formaintaining the state of the metal silicon within the raw material mixedproduct, that is, at the melting point of the metal silicon (1410° C.)or less. In this way, it is possible to obtain a silicon carbide powderhaving a particle diameter whereby the particle diameter of the metalsilicon source is maintained. The heating temperature is preferred to be1300° C. or more and 1400° C. or less. In addition, if the heatingtemperature is less than 1300° C., non-reacted metal silicon easilyremains which is not desirable.

Because the silicon carbide powder in the producing method of thepresent invention is obtained via a silicon carbide reaction due to asolid-phase-solid-phase reaction, the reaction rate is slow and themaximum heating temperature is preferred to be in a range of 4 hours ormore and 30 hours or less that non-reactive objects do not exist.

The silicon carbide powder to be obtained is a powder in which nano tosub-micron sized primary particles are sintered and secondary particlesbecomes a powder where the particle form of the metal silicon which isthe raw material is maintained. That is, it is possible to control theparticle diameter of the silicon carbide powder obtained from theparticle diameter of the raw material metal silicon.

In order to grow the primary particles of the obtained silicon carbidepowder, heating is performed at a higher temperature than the siliconcarbide formation temperature and maintained at this temperature as apost process. The heating temperature is preferred to be 1800° C. ormore and 2300° C. or less and more preferably 1900° C. or more and 2100°C. or less. If the heating temperature is less than 1800° C. or less,particle growth is insufficient and if the heating temperature exceeds2300° C., sublimation of the produced silicon carbide begins which isnot desirable.

The heating time in the post process is preferred to be in a range wherethe primary particles of the obtained silicon carbide powder aresufficiently grown and is preferred to be in range of 1 hour or more and10 hours or less and maintained at a maximum temperature.

In the producing method of the present invention, if the hearingconditions described above are satisfied then there is no particularimitation to the producing device and method of continuous producing.That is, heating and sintering in the silicon carbide production processand the heating in the post process may be performed continuously whilecontrolling the heating conditions in one heating furnace.

By performing a separation process of the obtained silicon carbidepowder using a sieve for example, a silicon carbide powder with anaverage particle diameter of 100 μm or more and 700 μm or less isobtained.

A silicon carbide single crustal can be obtained from the siliconcarbide powder of the present invention using a Modified Lely Method. Inthe Modified Lely Method, a seed crystal is placed on a part of a lid ofa graphite container, the silicon carbide powder of the presentinvention is filled into the graphite container and a single crystal isgrown by a sublimation recrystallization method.

EXAMPLES

Examples of the present invention are explained below. In addition, inthe present examples, produce of a silicon carbide single crystal wasattempted using a Modified Lely Method in order to confirm the effectsof the silicon carbide powder of the present invention.

Creation of Silicon Carbide Powder Sintered Powder Crushing MethodExample 1

The silicon carbide powder which is a raw material used the followingsynthesized product.

Metal silicon (silicon sludge, average particle diameter 1.0 μm, purity5N produced by Toshiba LSI) and acetylene black (denka black, averageparticle diameter 0.04 μm, produced by Denki Kagaku Kogyo) were weighedto produce a mol ratio (C/Si) of 1.0 between the raw materials siliconand carbon, and the raw material powder was adjusted after mixing usinga mortar in ethyl alcohol and dried. The raw material powder was putinto a graphite crucible, and the silicon carbide powder was obtained byheating in a carbon heater under an argon atmosphere at a temperature of1900° C. for 2 hours. The obtained silicon carbide powder was crystalphase analyzed using an X-ray diffractometer (MXP-3 produced by MacScience) and the powder was a β type (3C phase) silicon carbide.

In addition, a particle diameter distribution measurement was performedusing laser diffraction, scattering method using a particle sizedistribution measurement device (LS-230 produced by Beckman Coulter).Adjustment of the particle diameter distribution measurement sample wasperformed according to the measurement conditions of silicon nitride intable 1 of the attached explanation JIS R 1629˜1997 as a general ruleand the refraction index was 2.6. As a result the average particlediameter was 6.0 μm.

Next, the obtained silicon carbide powder is filled into a graphite moldwith an interior diameter of 50 mm and after preforming, a siliconcarbide sintered body was created by heating at 2200° C. for 2 hoursunder a pressure of 20 MPa in an argon atmosphere using a high frequencyinduction heating type hot press device. The density of the obtainedsintered body was measured using a dimensions, mass measurement and wasmeasured at 2.02 g/cm³ (absolute density 62.7%).

The created silicon carbide sintered body was crushed at a rotation rateof 2400 rpm using a micro-bantam mill (AP-B, produced byHosokawamicron). The crushed powder was separated using a sieve withgaps of 300 μm and 500 μm. As a result of separation, the yield ofpowder between 300 μm or more and 500 μm or less was 82%. Furthermore,the separated powder was heated at 60° C. in a mixed acid ofhydrofluoric acid, nitric acid and distilled water with a volume ratioof 1:1:1.

After thermolysis was performed on the obtained powder using a mixedacid of hydrofluoric acid, nitric acid and vitriolic acid, an impurityanalysis was performed using an ICP light emitting analyzer (CIROS-120produced by SPECTRO) and the contained amount of each impurity (Li, B,Na, Mg, Al, P, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Mo, Pd, Cd,Sb, Ba, W) was 1 ppm or less.

Particle size distribution was measure using a laser diffraction,scattering method using a particle size distribution measurement deviceand the average particle size was 449.7 μm.

Next, an SEM image observation of the powder was performed using ascanning electron microscope (SEM JSM-6390 produced by Nihon Denshi).The particle diameter of primary particles which were measured from theSEM image was 20 μm or more and 180 μm or less.

The specific surface area was measured using a constant volume type gasadsorption method using a specific surface area measurement device(NOVA3000e produced by Sysmex) and calculated using a BET multi-pointmethod. Furthermore, the measurement sample was aerated at 200° C. for 3hours in an N₂ flow atmosphere in advance. The specific surface area ofthe silicon carbide powder of the Example obtained in this way was 0.15m²/g. The properties of the powder are shown in FIG. 1.

Example 2

Silicon carbide powder (15H2, average particle diameter 0.5 μm producedby Pacific Rundum Co., Ltd) was filled into a graphite mold and afterpreforming, a silicon carbide sintered body was obtained by heatingunder an argon atmosphere at a temperature of 2000° C. for 2 hours at apressure of 30 MPa using a high frequency induction heating type hotpress device. The density of the obtained sintered body was measuredusing a dimensions, mass measurement and was measured at 1.95 g/cm³(absolute density 60.5%). A similar process as in Example 1 wasperformed on the created silicon carbide sintered body to obtain asilicon carbide powder. The obtained powder characteristics are shown inFIG. 1 the same as Example 1.

Example 3

Silicon carbide powder (T-1, average particle diameter 0.03 μm producedby Sumitomo Osaka Cement) was filled into a 50 mm interior diametergraphite mold and after preforming, a silicon carbide sintered body wasobtained by heating under an argon atmosphere at a temperature of 2200°C. for 2 hours at a pressure of 20 MPa using a high frequency inductionheating type hot press device. The density of the obtained sintered bodywas measured using a dimensions, mass measurement and was measured at1.37 g/cm³ (absolute density 42.4%). A similar process as in Example 1was performed on the created silicon carbide sintered body to obtain asilicon carbide powder. The obtained powder characteristics are shown inFIG. 1 the same as Example 1.

Example 4 Comparative Examples 1˜3

Example 4 and Comparative Examples 1˜3 were performed using the samemethod as Example 1. Each condition of the samples, sinteringconditions, sintering characteristics and powder characteristics areshown in FIG. 1 the same as in Example 1.

Comparative Examples 4

Apart from adding 0.5% by mass of boron carbide (HD20 average particlesize 0.5 μm produced by H.C. Starck) as a sintered auxiliary agent, thesame processes were performed as in Example 2. The results are shown inFIG. 1 the same as Example 1. The specific surface area of the siliconcarbide powder after crushing was below a measurement minimum.(measurement minimum 0.01 m²/g) In addition, 3400 ppm of boron wasincluded as a result of an impurity analysis using an ICP light emittinganalyzer.

As is clear from FIG. 1, the silicon carbide powder in Examples 1˜4obtained by the method of the present invention has a sufficient averageparticle diameter and specific surface area and few containedimpurities. However, the sintered body created according to theconditions in Examples 3 and 4 had low strength and the yield of theobtained silicon carbide powder was low. On the other hand, a sinteredbody could not be created in Comparative Examples 1˜3 and impuritieswere contained in Comparative Example 4.

Nucleus Addition Method Example 5 1. Synthesis of a Raw Material SiliconCarbide

Metal silicon and acetylene black were weighed to produce a mol ratio(C/Si) of elements of 1.0 between silicon and carbon, and the rawmaterial powder (raw material powder A) was adjusted after mixing usinga mortar in ethyl alcohol and dried. The raw material powder A was putinto a graphite crucible, and the silicon carbide powder a was obtainedby heating in a carbon heater under an argon atmosphere at a temperatureof 2000° C. for 2 hours. The average particle diameter of the obtainedsilicon carbide powder a was 17.5 μm. Furthermore, 10% by mass of theraw material silicon carbide powder was added to the raw material powderA, heating and sintering were performed by the process described aboveand a raw material silicon carbide b was obtained. The average particlediameter of the obtained raw material silicon carbide b was 44.8 μm.

2. Synthesis of Silicon Carbide Powder

Next, 10% by mass of the raw material silicon carbide b was added withrespect to the raw material powder A with a C/Si ratio of 1.0, and theraw material powder (raw material powder B) was adjusted after mixingusing a mortar in ethyl alcohol and dried. The raw material B wasinserted into a graphite crucible and silicon carbide powder wasobtained by heating in a carbon heater under an argon atmosphere at atemperature of 2000° C. for 8 hours.

The obtained silicon carbide powder was separated by passing through asieve with 125 μm gaps. The yield at 125 μm or more was 88%.

The average particle diameter of the obtained silicon carbide powder was163.2 μm and the specific surface area was 0.26 m²/g. In addition, anSEM image observation was performed and the particle diameter of primaryparticles which were measured from the SEM image was 10 μm or more and40 μm or less. Furthermore, as a result of a crystal phase analysis, allof the silicon carbides were β types (3C phase) and an impurity analysiswas performed using an ICP light emitting analyzer and the containedamount of each impurity was 1 ppm or less.

Examples 6˜8 Comparative Examples 5˜8 1. Synthesis of Raw MaterialSilicon Carbide

A raw material silicon carbide powder added in Examples 6˜8 andComparative Examples 5˜8 was obtained by repeating the processes by thesame method as in Example 5a plurality of times. The heatingtemperature, the number of times each process was repeated andcharacteristics of the raw material silicon carbide powder are shown inFIG. 2.

2. Synthesis of Silicon Carbide Powder

Apart from the average particle size and added amounts of the rawmaterial silicon carbide powder added shown in FIG. 2, the powder wascreated by the same method as in Example 5. The heating temperature andcharacteristics of the obtained silicon carbide powder are shown in FIG.2.

As is clear from FIG. 2, the silicon carbide powder in Examples 5˜8obtained by the method of the present invention has a sufficient averageparticle diameter and specific surface area. However, in Example 8, itwas clear that the powder characteristics did not show large effectscompared to the added raw material silicon carbide powder. However, thesilicon carbide powder in Comparative Examples 5˜8 had a small particlediameter.

Solid-Phase Reaction Method Example 9

45% by mass of a metal silicon (purity 5N produced by Kojundo ChemicalCo) with an average particle diameter of 308.2 μm and 55% by mass of aresol type phenol resin (J-325 produced by DIC) were mixed in ethylalcohol and after removing the solvent a raw material mixed product wasobtained by heat curing at 130° C. This was carbonized by heating for 1hour at 1000° C. under an argon atmosphere. The obtained carbide rawmaterial mixed product was analyzed for elements using an Igniting—IRmethod (IR-412 Produced by LECO) and a dehydration weight ICP lightemission analysis combined method (CIROS-120, compliant to JIS 1616produced by SPECTRO) and the C/Si was 1.12.

The obtained carbide raw material mixed product was put into a graphitecrucible and a silicon carbide powder was obtained by heating for 10hours at 1400° C. under an argon atmosphere. As a result of a crystalphase analysis of the obtained silicon carbide, there was no non-reactedsilicon or carbon and only β type (3C phase) silicon carbon. Inaddition, the average particle diameter was 289.4 μm.

Furthermore, the obtained silicon carbide powder was put into a graphitecrucible and heated for 2 hours at 2000° C. under an argon atmosphere ina carbon heater furnace. The average particle diameter of the heatedpowder was 284.1 μm and the specific surface area was 0.21 m²/g. Inaddition, an SEM image observation was performed and the particlediameter of primary particles which were measured from the SEM image was8 μm or more and 50 μm or less. Furthermore, an impurity analysis wasperformed using an ICP light emitting analyzer and the contained amountof each impurity was 1 ppm or less.

Example 10 Comparative Examples 9˜13

Example 10 and Comparative Examples 9˜13 were performed using the samemethod as Example 9. Each condition of the raw material in the sinteringprocess of the silicon carbide, sintering conditions and post processsintering conditions and characteristics of the obtained silicon carbidepowder are shown in FIG. 3.

Comparative Examples 14

Apart from using carbon black as the carbon source, the powder wascreated using the same method as Example 9. The characteristics of theobtained silicon carbide powder are shown in FIG. 3.

As is clear from FIG. 3, the silicon carbide powder in Examples 9 and 10obtained by the method of the present invention has a sufficient averageparticle diameter and specific surface area. However, in the ComparativeExamples 9, 12 and 14, the average particle diameter of the siliconcarbide powder after the silicon carbide sintering process was small andthe particle was also insufficient after post processing. In addition,in Comparative Example 13, the primary particle diameter was small andsintering between particles was weak making the powder easy to fallapart. In Comparative Example 10, it was clear that non-reacted siliconremained and in Comparative Example 11 silicon carbide was not produced.

Creation of Silicon Carbon Single Crystal Example 11

5 g of the silicon carbide powder created in Example 1 was filled into agraphite crucible with an 11 inch interior diameter. Next, a 4H—SiC(0001) single crystal plate was placed on a lid section as a seedcrystal. The graphite crucible was placed into a high frequencyinduction heating heater and after sufficiently performing argonreplacement, a single crystal was cultivated with an atmosphere pressureof 10 Torr and the bottom surface temperature of the crucible containerset at 2000° C. The sublimation rate after 2 hours of growth and after20 hours of growth and length of the single crystal after 20 hours ofgrowth are shown in FIG. 4. Here, the sublimation rate is a valuecalculated by dividing the reduced amount (sublimation amount) of theraw material silicon carbide powder after heating by the growth timeperiod.

Comparative Example 15

A single crystal was grown using the same method as in Example 11 usinga commercially available high grade purity silicon carbide powder(GMF-CVD produced by Pacific Rundum Co., Ltd). The average particlediameter of the raw material silicon carbide was 682.9 μm and thespecific surface area was below a minimum measurement. (below 0.01 m²/g)The results are shown in FIG. 4 the same as Example 11.

Comparative Example 16

A single crystal was grown using the same method as in Example 11 usinga commercially available polishing silicon carbide powder (NC-F8produced by Pacific Rundum Co., Ltd). The average particle diameter ofthe raw material silicon carbide was 2350 μm and the specific surfacearea was below a minimum measurement. (below 0.01 m²/g) The results areshown in FIG. 4 the same as Example 11.

Comparative Example 17

A single crystal was grown using the same method as in Example 11 usinga high grade purity silicon carbide powder (15H2 produced by PacificRundum Co., Ltd). The average particle diameter of the raw materialsilicon carbide was 0.5 μm and the specific surface area was 16.1 m²/g.The results are shown in FIG. 4 the same as Example 11.

Examples 12˜16 Comparative Examples 18˜20

A single crystal was grown using the same method as in Example 11 usingthe silicon carbide powder created in the Examples 2, 5, 6, 9 and 10,and Comparative Examples 5, 6 and 9. The results of the raw materialcharacteristics and after single crystal growth are shown in FIG. 4 thesame as Example 11.

As is clear from FIG. 4, in the Examples 11˜16 using the silicon carbidepowder in Examples 1, 2, 5, 6, 9 and 10 obtained using the method of thepresent invention, the raw material silicon carbide was sublimated at astable rate and a single crystal was grown without a reduction in thesublimation rate over 20 hours compared to a sublimation rate over agrowth period of 2 hours. However, in Comparative example 15, although araw material silicon carbide was sublimated at a stable rate, the rawmaterial sublimation amount was less than the silicon carbide powdercreated using the method of the present invention. In addition, inComparative Example 16 which used a raw material silicon carbide with alarge particle diameter, the amount of sublimation was small and thesingle crystal growth was 1 mm or less. In the Comparative Examples 17which used a raw material silicon carbide with a small particle diameterand the Comparative Examples 18˜20 which used the silicon carbide powderin Comparative Examples 5, 6 and 9, it was clear that the sublimationrate decreased after 20 hours of crystal growth.

The silicon carbide powder for the production of a silicon carbidesingle crystal of the present invention displays a high and stablesublimation rate during single crystal growth.

INDUSTRIAL APPLICABILITY

The silicon carbide powder of the present invention displays a high andstable sublimation rate during a sublimation recrystallization methodand can be favorably used as a raw material for a silicon carbide singlecrystal.

1. A silicon carbide powder for producing a silicon carbide singlecrystal comprising: an average particle diameter of 100 μm or more and700 μm or less and a specific surface area of 0.05 m²/g or more and 0.30m²/g or less.
 2. The silicon carbide powder for producing a siliconcarbide single crystal according to claim 1, wherein primary particleshaving an average particle diameter of 5 μm or more and 200 μm or lessare sintered.
 3. A method for producing a silicon carbide powder for theproduction of the silicon carbide single crystal according to claim 1further comprising: sintering a silicon carbide powder having an averageparticle diameter of 20 μm or less under pressure of 70 MPa or less at atemperature of 1900° C. or more and 2400° C. or less and in anon-oxidizing atmosphere, thereby obtaining a sintered body having adensity of 1.29 g/cm³ or more; adjusting particle size by means ofpulverization of the sintered body; and removing impurities by means ofan acid treatment.
 4. The method for producing a silicon carbide powderfor the production of a silicon carbide single crystal according toclaim 1, wherein the silicon carbide powder is obtained by heating andsintering a raw material mixed product at a temperature of 1800° C. ormore and 2300° C. or less under a non-oxidizing atmosphere conditionusing 5% by mass or more and 50% by mass or less of a silicon carbidepowder with average particle diameter of 20 μm or more with a siliconsource and a carbon source.
 5. The method for producing a siliconcarbide powder for the production of a silicon carbide single crystalaccording to claim 1, further comprising: producing the silicon carbidepowder by heating and sintering metal silicon and a carbon source withan average particle diameter of 100 μm or more and 700 μm or less undera non-oxidizing atmosphere condition at a temperature of 1300° C. ormore and 1400° C. or less; and post-processing the silicon carbidepowder by heating at a temperature of 1800° C. or more and 2300° C. orless under a non-oxidizing atmosphere condition.
 6. The method forproducing a silicon carbide powder for the production of a siliconcarbide single crystal according to claim 5, wherein the carbon sourceis an organic compound and the organic compound is carbonized by heatingat a temperature of 500° C. or more and 1000° C. or less under anon-oxidizing atmosphere condition before producing the silicon carbidepowder by heating and sintering.